260 
THE STUDY OP THE SCIENCE OP BOTANY. 
principle, not yet determined by chemists, and varying in the degree 
of abundance in which it is found in different species. It is particu¬ 
larly abundant in the seeds of mustard and garden rocket, in the roots 
of horse-radish, and in the foliage of the Lepidium latifolium, which, 
administered inwardly, acts powerfully upon the gastric organs, or, 
applied outwardly, inflames the skin, and operates nearly as severely as 
blisters. 
Cruciferous plants are chiefly natives of temperate climes, those 
which are found within the tropics being, in all cases, mountain plants, 
and are nearly all cultivated in the open air; they are mostly found in 
open sandy plains, some on the tops of the highest mountains, at the 
utmost limits of vegetation. Nearly 1000 species are now described, 
of which not more than twenty-two are to be found in the works of 
Hippocrates, Theophrastes, Dioscorides, or Pliny. 
The flowers of this class are of a particular structure, answering to 
the following characters: — 
Calyx. A perianthium, tetraphyllous and oblong, the leaves of 
which are ovate-oblong, concave, obtuse, conniving, gibbous downwards 
at the base; the opposite ones equal and deciduous. Within the calyx 
of these flowers is a nectarium, which is the reason of the base being 
gibbous. 
Corolla . Called cruciform; four equal petals ; the claws piano- 
subulate, erect, somewhat longer than the calyx. The limb plain ; the 
laminae widening outwards, obtuse, the sides hardly touching one 
another. The insertion of the petals is in the same circle with the 
stamina. 
Stamina. The filaments six, and subulate, of which two that are 
opposite are of the length of the calyx ; the other four somewhat longer, 
but not so long as the corolla. The anthera oblong, acuminate, thicker 
at the base, erect, and with their tops leaning outwards. There is a 
nectariferous glandule, which, in the different genera, has various 
appearances; it is seated.close to the stamina, and particularly to the 
two shorter ones, to whose base it is fastened ; and these have a slight 
curvature to prevent their pressing upon it, whereby those filaments 
become shorter than the rest. 
Pistillum. The germen above the receptacle increasing daily in 
height. The style either of the length of the longer stamina or wanting. 
The stigma obtuse. 
Pericarpium. A siliqua of two valves, often bilocular, opening from 
the base to the top of the dissepiment, and projecting at the top beyond 
the valves, the prominent part of these having before served as a style. 
